My invention relates generally to an apparatus, generally known as a disk drive, for reading and/or writing data on a recording disk such as a flexible magnetic disk. More particularly, my invention pertains to an apparatus in such a disk drive for centering and clamping the recording disk in a preassigned position for data transfer with a transducer or a pair of transducers. Still more particularly, my invention concerns improvements in or relating to the disk centering and clamping apparatus described and claimed in U.S. Pat. No. 4,689,782 filed by Tsuchiya et al. and assigned to the assignee of the instant application.
I know several devices heretofore suggested and used for centering and clamping a flexible magnetic disk in a disk drive. Generally, such devices comprise a rotary clamp in the form of a tapered collet which is both rotatable about its own axis and movable into and out of engagement with a socketed drive hub rigidly mounted on a motor driven shaft. U.S. Pat. No. 3,768,815 to Mathurin teaches the radial splitting of the collet into several segments. The collet segments are wedged apart against the inner wall of the drive hub defining the socket, in order that the magnetic disk may be captured between collet and hub in axial alignment therewith. However, the use of the wedging means, as well as of the release springs associated with the collet, according to Mathurin makes his apparatus expensive in construction and difficult of assemblage.
One solution to the problem of how to simplify the construction of disk centering and clamping apparatus is found in Japanese Utility Model Publication No. 58-22318. It teaches a contractible collet that is pressfitted in the hub socket.
The above cross referenced U.S. Pat. No. 4,689,782 to Tsuchiya et al. represents another solution to the problem. Tsuchiya et al. also employs a segmented collet, with each segment including a deflectable, arched bridge portion joining the body portion of the clamp to one of the disk centering and clamping portions of annular arrangement. The arched resilient bridge portions enable the centering and clamping portions to positively clamp the disk even though the annular disk bearing surface of the drive hub, the substantially annular disk clamping surface of the collet, and the mangetic disk to be clamped may not necessarily be each absolutely flat.
I have found a weakness in this Tsuchiya et al. device. The weakness arises from the fact that, typically molded of a rigid plastic, the clamp is subject to change in size with ambient temperatures. The centering portions of the clamp on thermal expansion will not easily fit in the socket in the drive hub. On thermal contraction, then, the centering portions of the clamp will have play with respect to the drive hub socket, with the consequent possibility of disk misalignment on the hub. An obvious remedy for this weakness might be to make the centering portions large enough to fit closely in the hub socket even at low temperatures and, at the same time, to increase the elasticity of the bridge portions. Then the centering portions would elastically fit in the hub socket even at high temperatures. However, such an increase in the elasticity of the bridge portions would invite a decrease in the force under which the clamping portions of the clamp urge the disk against the drive hub.